Air conditioning

I have 2003 Ford Ranger 4.0, my air conditioner wasn't blowing cold air, I took it to the dealer the mechanic told me that the compressor clutch had falling off and I should replace the compressor and clutch for about $1,000.00. I took the car home, asked my week end mechanic friend, he said I could just replace the clutch, since only the outside part of the clutch is missing, the pulley and other piece are still there. Can I just replace the outside piece or do I have to replace the whole clutch assembly?

Thanks